System and method for state monitoring of linear drives of stretching and/or blow moulding machines

Abstract

A linear drive for a stretch and/or blow moulding machine has a force sensor for detecting actual force absorption of the linear drive during operation, a storage device in which data for a desired force absorption during operation are stored, and a comparison device for comparing actual force absorption with desired force absorption and a signal emitter for outputting a signal if a previously defined deviation between desired force absorption and actual force absorption is exceeded. Also provided is a method for determining a friction coefficient of a linear drive for a stretching and/or blow moulding machine, by determining a desired force absorption of the linear drive during operation, detecting using a force sensor, actual force absorption of the linear drive during operation, comparing actual force absorption with desired force absorption, and outputting a signal if a previously defined deviation between desired force absorption and actual force absorption is exceeded.

The invention claimed is: 
     
       1. A method for determination of a friction coefficient of a linear drive for a stretching and/or blow moulding machine, comprising the following steps:
 determining a desired force absorption of the linear drive during operation, 
 determining an actual force absorption of the linear drive during operation using a force sensor, 
 comparing the actual force absorption with the desired force absorption, and 
 outputting a signal when a previously defined deviation between desired force absorption and actual force absorption is exceeded, wherein the data for a desired force absorption of the linear drive during operation are calculated from parameters which are selected from a group consisting of a weight force of the moving parts, an inertial force of the moving parts depending upon an underlying movement profile, a pressure prevailing in the container or the preform, pneumatically effective surfaces of the system and a frictional force of the stretching unit and from the parameters a model is calculated which includes a variable for the frictional force on the stretching unit and in a subsequent optimisation process simulations of the desired force absorption of the linear drive are carried out by variation of values for the frictional force simulation until a sufficiently good approximation between the simulation of the desired force absorption and the actual force absorption of the linear drive is achieved. 
 
     
     
       2. The method according to  claim 1 , wherein the force sensor detects current consumption necessary for movement of a stretching rod. 
     
     
       3. The method according to  claim 2 , wherein a time range of the process which is particularly suitable for identification of the friction coefficient is selected for comparison of the actual force absorption with the desired force absorption. 
     
     
       4. The method according to  claim 2 , wherein on the basis of the comparison of the actual force absorption with the desired force absorption a required maintenance cycle for the cleaning of the stretching unit is determined. 
     
     
       5. The method according to  claim 1 , wherein a time range of the process which is particularly suitable for identification of the friction coefficient is selected for comparison of the actual force absorption with the desired force absorption. 
     
     
       6. The method according to  claim 1 , wherein on the basis of the comparison of the actual force absorption with the desired force absorption a required maintenance cycle for the cleaning of the stretching unit is determined. 
     
     
       7. A linear drive for a stretch and/or blow moulding machine, said linear drive including a force sensor for detecting an actual force absorption of the linear drive during operation, a storage device in which data for a desired force absorption of the linear drive during operation are stored, a comparison device for comparing the actual force absorption with the desired force absorption, a signal emitter for outputting a signal if a previously defined deviation between the desired force absorption and actual force absorption is exceeded, and a data processing unit for calculating the data for a desired force absorption of the linear drive during operation from parameters which are selected from a group consisting of a weight force of the moving parts, an inertial force of the moving parts depending upon an underlying movement profile, a pressure prevailing in the container or the preform, pneumatically effective surfaces of the system and a frictional force of the stretching unit, and for calculating a model from the parameters which includes a variable for the frictional force on the stretching unit and for carrying out optimisation process simulations of the desired force absorption of the linear drive including variation of values for the frictional force simulation until a sufficiently good approximation between the simulation of the desired force absorption and the actual force absorption of the linear drive is achieved. 
     
     
       8. The linear drive according to  claim 7 , wherein the force sensor is a detector for current consumption necessary for movement of stretching rod. 
     
     
       9. The linear drive according to  claim 7 , wherein the storage device comprises a plurality of data sets for the desired force absorption of the linear drive for different reshapings of preforms into containers.